Acrylonitrile-butadiene-styrene resins (also “ABS” resins) are used in a variety of applications including automobiles, electric and electronic equipment, business machinery, home appliances, toys, and the like due to their excellent impact resistance and workability, superior mechanical strength, thermal deformation temperature, and beautiful external appearance. However, ABS resins are easily deteriorated by sunlight and ultraviolet (UV) radiation since the butadiene-based rubber component used in the ABS resins comprises a chemically unstable double bond. Therefore, the use of ABS resins is limited for many products that are used outdoors and/or exposed to UV radiation, such as electric and electronic components, materials for farm machines and implements, road signboards, finishing materials for buildings, door panels, window frames, leisure/household goods, sports equipment, automobile supplies, and the like.
Weather resistant stabilizers can be added to ABS resins to improve weatherability. Techniques using weather resistant stabilizers can, however, have limited effectiveness. Accordingly, research efforts have looked to replacing ABS resins with acrylate-styrene-acrylonitrile (also “ASA” resins) resins, which include a chemically stable acrylic-based rubber instead of a butadiene-based rubber.
Recently, there has also been an increased focus on the development of thermoplastic resins that can be directly used without coating or painting due to environmental concerns. In addition, there is also increased demand for thermoplastic resins with low gloss characteristics in view of customer expectations, who often prefer the high-grade external appearance of low gloss products. For example, ASA resins used for outdoor applications can require low gloss characteristics.
Conventional methods for imparting a low gloss appearance to the surface of molded articles include embossing a surface of a molded article and coating the surface of the molded article with a low gloss material. The processing costs for such methods, however, can be expensive. Further, such methods may not sufficiently lower surface gloss. Therefore, there have been attempts to modify the ASA resins themselves to impart sufficiently low gloss characteristics.
U.S. Pat. No. 6,696,165 discloses a method for lowering the gloss of ASA resins by adding 0.1 to 20 parts by weight of a crystalline polymer such as a polyalkyl terephthalate, and U.S. Pat. No. 6,395,828 discloses a method for lowering the gloss of ASA resins by adding 0.5 to 15 parts by weight of a compound prepared by a reaction of an amine compound with epoxy.
U.S. Pat. Nos. 5,475,053 and 4,652,614 disclose methods of lowering the gloss of resins by using spherical graft copolymers as matting agents, and U.S. Pat. Nos. 4,169,869, 4,460,742 and 5,580,924, and Korean Patent Laid-Open Publication No. 2008-0036790 disclose methods of lowering the gloss of resins by using a variety of copolymers as additives.
Further, U.S. Pat. Nos. 4,668,737 and 5,237,004 disclose methods of lowering the gloss of resins by using rubber particles having a core/shell structure with a large particle diameter range of 0.05 to 20 μm or 2 to 15 μm.
However, problems including high production costs, delamination, property deterioration and partially increased gloss may occur when the additives are used as in the foregoing techniques. In addition, the use of large rubber particles can rapidly deteriorate the impact strength of the resins although the gloss of the resins can be advantageously lowered.
U.S. Pat. Nos. 3,426,101 and 6,187,862, Japanese Patent Laid-Open Publication No. Hei 7-316243, Korean Patent No. 10-0440474, and Korean Patent Application No. 2006-0051425 are directed to methods of preparing ASA resins by conventional techniques generally comprising the steps of preparing an alkyl acrylate-based latex core, preparing a graft polymer by graft polymerizing styrene and acrylonitrile on an outer layer of the core, and melting and kneading (mixing) the prepared graft polymer and a styrene-based thermoplastic resin. However, such methods of preparing the ASA resins use multiple steps which can increase production costs. Further such methods typically use a variety of emulsifiers and stabilizers to prepare the latex, which can deteriorate color characteristics.
U.S. Pat. Nos. 5,910,553, 6,111,024, and 6,051,656 disclose methods of preparing ASA resins by preparing alkyl acrylate copolymers through solution polymerization, drying the alkyl acrylate copolymers, performing bulk polymerization by injecting the dried alkyl acrylate copolymers into styrene-based monomers and acrylonitrile-based monomers, and converting the bulk polymerization into the suspension polymerization. However, these methods are not commercially viable, and there is the further drawback of additionally requiring a process to recover the final product from a suspension.
As discussed in the foregoing, despite the many attempts to provide ASA resins with excellent weatherability and low gloss characteristics, conventional techniques do not provide sufficient weatherability and gloss properties.